http://www.maxxis.com/Bicycle/Technology.aspx
I'm not sure why the Sales Dept. decided to stop publishing the durometer of the compounds used. It isn't a secret, and it tells very little about the properties of the compound other than its hardness. But it is useful in a way. So for those interested:
3C MaxxSpeed = 70a base layer, 62a outer center layer, 60a outer shoulder layer
3C MaxxTerra = 70a base layer, 50a outer center layer, 42a outer shoulder layer
3C MaxxGrip = 70a base layer, 42a outer center layer, 40a outer shoulder layer (the same configuration it's always been)
Questo e' tutto quello che ho trovato in giro.